This preview shows page 1. Sign up to view the full content.
17. (a) If the system of three charges is to be in equilibrium, the force on each charge
must be zero. The third charge
q
3
must lie between the other two or else the forces acting
on it due to the other charges would be in the same direction and
q
3
could not be in
equilibrium. Suppose
q
3
is at a distance
x
from
q
, and
L
–
x
from 4.00
q
. The force acting
on it is then given by
()
33
3
2
2
0
4
1
4
qq
qq
F
x
Lx
πε
§·
=−
¨¸
−
©¹
where the positive direction is rightward. We require
F
3
= 0 and solve for
x
. Canceling
common factors yields 1/
x
2
= 4/(
L
–
x
)
2
and taking the square root yields 1/
x
= 2/(
L
–
x
).
The solution is
x
=
L
/3.
The force on
q
is
2
3
22
0
14
.
0
0
.
4
q
qq
q
F
xL
ε
−
=+
π
The signs are chosen so that a negative force value would cause
This is the end of the preview. Sign up
to
access the rest of the document.
 Spring '09
 Bolton
 Charge, Force

Click to edit the document details